This invention relates to a non-directional pneumatic agricultural tire for use on farm tractors and similar agricultural type vehicles. Tractor tires must have good vibration characteristics on and off the road while maintaining good traction or drawbar characteristics. Such tires must also provide for the removal of soil, mud, etc., during in-field use.
In the past, agricultural vehicles were horse drawn. With the introduction of motorized tractors in the early 1900's the farm wheels were made of steel with traction cleats extending across the steel wheel. E. J. Farkas in 1922 patented a detachable tread for tractor wheels. U.S. Pat. No. 1,423,519 describes a rubber tread member that could be added to the steel cleat thus making it possible to cross a road without destroying the paved surface. These historical vehicles were greatly underpowered for the task of farming. Accordingly, the wheels were generally designed to be somewhat, if not entirely, non-directional with cleats inclined or normal to the direction of travel. The non-directional characteristic was helpful when the tractor became stuck. In such cases, horses would be hooked to the rear of the vehicle and the tractor with the assistance of added horsepower could reverse itself out of the muck.
As tractor motors improved, the tires became directional in design. The tractor's primary function required forward pulling power and tires were accordingly designed to enhance this feature.
In 1942, James E. Hale, a farm tire engineer, developed a pneumatic tire for heavy muck. U.S. Pat. No. 2,271,337 describes an attempt to design a non-directional tire having a central rib. Hale's tire, although noted to be non-directional, was also noted to be self-cleaning in only one direction on each side of the tire. This mud packing characteristic was a common problem of all tractor tires but is particularly troublesome for non-directional tractor tires.
As the agricultural tires advanced in design and construction, the tire art field has become one of almost exclusively directional tread patterns.
The related art field of earthmover tires, although being somewhat directional in tread design, employs more tread patterns that are non-directional. Earthmover tires generally have a more closed tread pattern exhibiting net-to-gross ratios above 40%, whereas agricultural tires are more open having net-to-gross ratios of less than 40%, typically less than 30%. A 1974 U.S. Pat. No. 3,844,326 depicts a lugged tire for heavy construction equipment employing a nondirectional type pattern.
Similarly, a U.S. design patent 178,166 displays a multilug non-directional pattern. These type tread patterns commonly employ an increased net-to-gross ratio in the center of the tread and lugs having a lug width at the radially outer surface greater than two-thirds of the radial height of the lug. Designed for durability under heavily loaded off-road conditions, earthmover tires can accept some levels of mud packing in the center of the tread. Recently a new type farm tractor has been developed that will require substantially equivalent forward and reverse traction under load. These multipurpose tractors will accordingly require a non-directional tread pattern.